1. Field of the Invention
The present invention relates to a method of and an apparatus for attaching a base to a Braun tube by means of an adhesive resin and then effecting knocking and, more particularly, to a method of and an apparatus for bonding a base to a Braun tube by drying and hardening or curing such an adhesive resin.
2. Description of the Related Art
In typical Braun-tube manufacturing processes, after completion of evacuation, Braun tubes are subjected to pre-knocking, activation of cathodes, aging of electron guns, and post-knocking.
Related art which will be described hereinafter with reference to FIGS. 7 and 8 is one of the techniques which had been secretly carried out when the present inventors made the invention, but the present inventors have not found any written publication which indicates that such a related art is publicly known.
As shown in FIG. 7, the step of attaching a base 102 to a Braun tube 101 by means of an adhesive resin 103 is performed after the step of exhaustion. In this case, the knocking and aging steps of the electron gun are carried out while the Braun tube 101 is being conveyed which is suspended from a trolley hanger 104 with its faceplate 120 facing up. Drying and curing of the adhesive resin 103 interposed between the Braun tube 101 and the base 102 is carried out by naturally drying the adhesive resin 103 while the Braun tube 101 is suspended from the trolley hanger 104.
In such related art, however, since the adhesive resin 103 is dried by natural drying process, such a drying step requires a long time period and, therefore, the productivity is low. Further, since the adhesive resin 103 is naturally dried while the Braun tube 101 is being conveyed with the base 102 facing down, the base 102 may be deviated from a predetermined mounting position on the Braun tube 101. Furthermore, if the adhesive resin 103 does not satisfactorily dry, the position of the base 102 may be deviated, as shown in FIG. 8, due to its weight or vibration. If a knocking voltage is applied across electrodes for cleaning when the adhesive resin 103 still contains moisture, the internal resistances among a plurality of pin terminals 127 connected to the socket 105 decrease under the influence of water or an acidic solution contained in the adhesive 103, and a proper knocking voltage may not be applied across the electrodes.
In general, in order to increase the withstand voltage among the pins 127 connected to the socket 105 after the drying step, a silicone-type resin solution (semisolid) is used as an adhesive. Particularly in recent years, the high voltage of Braun tubes has been increased from 25 to 30 kV or higher. Accordingly, it has become important for the withstand voltage of the insulation resistance among electrodes to be kept sufficiently high. Therefore, it is desired to solve the above-described problems.
Japanese Patent Examined Publication No. 29-6510 discloses a method of bonding a base to the bulb of an electron tube such as a vacuum tube by using an adhesive. The method comprises the steps of embedding in advance a metal ring in the adhesive, supplying high-frequency electromagnetic energy to the metal ring to cause induction heating therein, heating the adhesive from the inside thereof, and hardening the adhesive.
The disclosed technique is suitable for application to tubes such as vacuum tubes of low anode or plate voltage, but it is not practical to apply the art to Braun tubes because of the low withstand voltage among pin terminals.
Japanese Patent Unexamined Publication No. 59-119656 (corresponding to GB 2,132,012A) discloses a technique in which a protecting base having high withstand voltage characteristic is attached to an electron tube as rapidly as possible by directly forming the base by a casting process and covering a sealed exhaust portion formed at the end of the neck of the electron tube (a portion at which a thin tube part used for exhaustion of the electron tube is sealed).
However, the disclosed technique does not employ any adhesive resin, but may provide an obstacle to formation of a continuous manufacturing line. In addition, it would be difficult in this technique to firmly secure the protecting base to the body of an electron tube without a long exhaust portion.